In 2018, the focus of Honours
projects in the Plant Ecology Lab will firmly be on factors that affect species
distributions & abundance (change in climate, fire regimes, competitors)
and the plant population dynamics that underpin these processes. One of the key
research questions in my Lab is: how do C4 grasses shape ecosystems
via their effects on fire regimes & competitive interactions, and how do
plants species in ecosystems respond to ecosystem drivers over decadal
timescales. These questions have important implications for how we view
ecosystem change, and management to maintain biodiversity. Below are some ideas
for projects. I am happy to discuss other projects with students whose broad
interests align with the types of research I undertake. Please contact me on J.Morgan@latrobe.edu.au.
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Project 1: How fire regimes can shift a biome.
In the tropical savanna of northern Australia, fire regimes shape the structure
and function of ecosystems. But what exactly is the mechanism and are feedback
loops involved? One clear pathway is that fire affects savanna “receptivity” to
establishment by Sorghum intrans (an
annual native C4 grass that establishes & persists under high light
environments; it seems not to like growing much under eucalypt canopies). This
alone, however, is probably only half the story. With an increase in Sorghum (dominance and extent), this
species likely changes the fire regime by increasing the intensity of fire,
further promoting this species over woody plants (by negatively affecting
mid-storey and overstorey woody plant cover and light interception). It may
also affect the distribution of other grass species because of a) competitive
effects and b) fire intensity effects. This simple (and oft-quoted) feedback is
poorly documented in the literature but can be directly tested in one of
Australia’s few long-term fire regimes experiments. At the Territory Wildlife
Park (Darwin), CSIRO and Charles Darwin University have been investigating how
fire regime (1, 2, 3, 5 yr burn frequency vs. unburnt controls) affects biota,
starting from a little burnt tropical ecosystem. The experiment has been going
for 15 yrs. Early studies (after just 4 yrs of the experimental implementation)
hint that Sorghum was increasing and
woody plants were in decline, but it was too early to determine whether fire
could switch the system from woody to grassy. In this study, we will build on
previous work and ask: what is the current extent of Sorghum and how does fire regime affect this relationship? How is Sorghum cover related to woody plant
cover (i.e. competition by canopy and mid-storey species for light)? How is
grass diversity distributed in relation to fire regime, and Sorghum dominance? How does Sorghum affect properties of fire such
as intensity? We will re-survey the plots to model changes in dominance over
time (ecological tipping points versus linear trend change) and how Sorghum affects fuel dynamics and fire
behaviour. Spatial patterns of Sorghum
versus woody (and other grass) plant cover will be investigated, possibly using
transplant experiments. The project involves a month of field work in Darwin.
Co-supervised with Dr Warren Paul (LTU – AW), Dr Anna Richards (CSIRO) and Dr Dick
Williams (CDU).
Note: Project 1a. I may also
have a project on faunal responses to fire in the Territory Wildlife Park. Arthropods
found in fire-adapted habitats have specific traits and dispersal strategies to
deal with frequent fires. For example, they seek refugia during fires where
temperatures may be lower. Refugia are areas adjacent to or within a burn area
that enhance arthropod survival during a fire, facilitate persistence of
individuals, or allow for post-fire recovery. These may include insulated
underground burrows, fire-resistant termite mounds, or patches of unburned vegetation.
Dispersal is another obvious response to fire for arthropods, and as a result,
winged orders have higher survivorship than less-mobile taxa. A couple of years
ago I observed, ahead of an experimental fire, insects, lizards and even frogs
moving up the trunk of a tree. They were clearly trying to get away from the
flame zone. What warning signals are they cueing into? This project will
quantify movement patterns up and down tree trunks, before and after fire in
frequently burned tropical savanna. Depending on what we find, we will try and
unravel the sensory cues that lead to this fire-scape behaviour. Co-supervised
with Dr Alan Andersen (CDU).
Project 2: Re-introducing fire
into long unburnt grassy ecosystems– accelerated recovery of the ecosystem, or
stasis? Many grasslands and grassy woodlands are now rarely burnt,
although it is likely that patch burning once played an important role in the
structure and function of these ecosystems. Fire exclusion has led to tree
recruitment, woody plant encroachment and loss of diversity. Land managers are
increasingly re-introducing fire to long unburned landscapes to promote
diversity, but what changes occur when fire is re-introduced to ecosystems when
it has been long absent? Are trees
resilient to fire (or does it depend on their size)? Do species appear that
haven’t been seen for a while, presumably re-appearing from dormant soil stored
seed? Do some species disappear, having initially profited from the absence of
fire? In this project, we will
test ideas about re-introduction of fire to landscapes where much benefit might
be derived from such activities. Grassy ecosystems in western Victoria are much
restricted (due to agriculture and, increasingly, timber plantations) and need
sympathetic management to maintain their natural values. Re–introducing
frequent fire to long unburnt grasslands is seen as a desirable management
activity – it should serve to open up opportunities for seed regeneration and
species coexistence. However, there are almost no examples where this has been
tested, at least in good quality vegetation. In this study, we will
burn long unburnt grasslands and ask whether often reported reductions in
species richness due to the cessation of frequent fire can be spontaneously
reversed by the return of fire. Additionally, will the abundance of currently
sparse species be improved? How will exotic species respond to a change in
disturbance regime? What about trees that have established in the inter-fire period?
The student will work closely with the CFA, who will be responsible for
conducting the trial burns, to design and implement the burning experiment.
Project 3: Banksia decline in
coastal grassy woodlands: encroaching shrubs and the water balance. Coastal
grassy woodlands have declined across much of their range. One main reason for
decline has been an increase in woody plants (like Coast Tea-tree, CTT) in the
decades where fire has been excluded from the ecosystem. Here, CTT shrubs have
established and infilled between trees, largely causing the elimination of the
ground flora. This process is now well-documented. What still mystifies
ecologists is the long-term decline of overstorey trees like Coast Banksia (Banksia integrifolia, Proteaceae), a foundation
species of grassy woodlands that can achieve i) enormous size, ii) store vast
amounts of carbon, iii) provide abundant floral resources for nectivores and
iv) important nesting sites via hollows. The decline of Coast Banksia in places
like Yanakie Isthmus and Oberon Bay at Wilsons Promontory National Park has
been a slow, drawn out process, with canopy loss and health the most obvious
sign of ill-health. Some studies have tried to understand why trees are in
decline – and to date, the answer has largely eluded researchers. We know that
it’s not a) mineral nutrition imbalances, b) root pathogens or c) disease. In
this study, we will explore the hypothesis that encroaching CTT shrubs have
reduced water availability to Coast Banksia, and that Coast Banksia surrounded
by dense CTT are under more water stress than trees in the absence of
encroaching CTT. This study will be the first to determine if water stress
could account for loss of canopy and necrotic foliage and, ultimately, to tree
mortality in what is a water-limited ecosystem (due to deep, well-drained calcareous
sands). We will examine soil water balance in areas with and without
encroaching CTT to determine how shrubs dry soils. We will investigate the
rooting depth profiles of Coast Banksia and CTT. Using an ecophysiological
approach, we will examine tree stress (particularly over summer) in a natural
experiment by quantifying leaf water potential, leaf gas exchange
parameters (net photosynthetic rate and stomatal conductance) and chlorophyll fluorescence
in areas with and without dense CTT. In a BACI experiment, we will remove
encroaching CTT shrubs around Banksia and / or use supplementary watering to
see if this changes the plant stress profile of Coast Banksia trees. Co-supervised
with Dr Pete Green.